Receiving system



June 2, 1936. M. G. CROSBY RECEIVING SYSTEM Filed May 28, 1934 5Sheets-Sheet l June 2, 1936. M. .G. cRbsBY 2,042,831

RECEIVING SYSTEM Filed May 28, 1934 5 Sheets-Sheet 2 3: a: I'M- 5E 91*INVENTOR f MURRAY 6. CROSBY ATTORN EY June 2, 1936. G CROSBY 2,042,831

RECEIVING SYSTEM Filed May 28, 1934 5 Sheets-Sheet 3 /KZW ATTORNEYjAAAll I'I'I Allll IIVII m QQ Ba 71 we; 56 Q I T MN wv v 37 a E w Q\ w NJune 2, 19 36. M. G. CROSBY RECEIVING SYSTEM Filed May 28, 1934 5Sheets-Sheet 4 ATTORNEY June 2, 1936. M e. CROSBY RECEIVING SYSTEM FiledMay 28, 1934 5 Sheets-Sheet 5 Patented June 2, 1936 iii? 'i'A'i'S A'EENTFFlE RECEIVING SYSTEM Delaware Application May 28, 1934, Serial No.727,931

17 Claims.

My present invention relates to a radio receiving system and has as itsprincipal object the provision of a system wherein energy received fromthe antennae of a diversity array is combined in phase at all times.

A further and more specific object is to provide a system wherein thephase relation of currents derived from a diversity antenna system aremaintained at a constant value so that currents derived from theantennae may be combined as though the phase of each antenna remainedconstant.

More fully, in the prior art of diversity reception there are two wellknown methods of combining the energies received from antennas havingdifierent fading characteristics. The first is rectifying the antennaeenergies and then combining the rectified energies; and the second is bymeans of an automatic volume control arrangement which automaticallyshuts off the amplifiers from all the antennas but the one having thestrongest signal.

The first of these two systems of combination, namely, the combinationof the rectified energies, is limited mostly to CW telegraphy circuitswhere the rate of modulation is not too high. Under certain atmosphericconditions and upon certain radiation frequencies (those in the vicinityof 20 megacycles and higher) direct combination of the rectified outputsof voice and music modulation feasible; however, the tendency is towardthe second method of combination for these types of modulation. In fact,at the present timepractically all the voice and music diversity systemsutilize the automatic volume control antenna choosing system.

Thus, prior diversity systems have combined the energies from theantennas by the addition of rectified outputs or by a choosing devicewhereby only a single antenna was made operative at one time. Hence, theantennas do not combine to improve directivity as would be the case ifthe radio or intermediate frequency energies were combined as they arein a broadside array. Such a combination of antennas giving a diversityciiect has been impossible due to the fact that the phase or" theenergies from the various antennas does not remain constant, at thevalue which the spacing and combination circuits determine, but varyrelatively with fading. Consequently, a combination which might beeffective at one instance of time might be ineffective at another as thefading progressed.

In the invention herein described means are provided for combining theR. F. or I. F. energies in a diversity system so that the system, in-

stead of having a directivity equivalent to that of a single antenna,has a directivity equivalent to a combination of all of the antennas.The

phases of the energies from each antenna are automatically controlled sothat the phase of combination is always proper. Hence, a superdirectivesystem is obtained which has all the advantages of the prior diversitysystems.

A further advantage of the system herein described is that it may beutilized to effect a directive system which automatically changes itsdirectivity in accordance with the changes in the bearing of the signal.Thus, as the signal comes in from different directions the antennasystem auto- .2 Figures 1, 1a, 2, 3, 4 and 5 show schematic diagrams ofvarious modifications of the fundamental idea. That is, Figure 1 showsan arrangement whereby the two antennae are held in phase by means of amotor operated phase shifter. Figure '10. gives an auxiliary combiningarrangement to be used on the circuits of Figures 1, 2, 3 and 5. Figure2 portrays a method of phasing whereby the frequency of one of the highfrequency oscillators is varied to maintain phase synchronism of the twosignals. Figure 3 shows a three receiver diversity system wherein thevarious signal I. F. energies are held in phase with an I. F. os-

the differential detector energy to vary the frequency of the commonsecond I. F. oscillator. Figure 6 and the vector diagrams of Figures 7,8, 9 and 10 are used in the explanation of the operation of thedifferential detectors.

In Figure 1 the two heterodyne receivers 2, 3

All

cillator, with a filtered and limited carrier, or

phase'shifting unit in the dotted line enclosure,

The energy from I. F. amplifier 5 is fed via Transformer l6 feeds 0!).line 15 to transformer i6.

coupling tubes I? and i8 having tuned circuits,

I9 and 2:; in their plate circuits. The tunings of 19 and-2B areadjusted so that their Voltages, in-

duced in coupling coil 2|, are 98 degrees out of phase, thus eflecting aphase shifter.

Coil 2|, which feeds transformer 1, is mounted on shaft 22 in bearing23.on the other end of shaft 22 is a friction drive wheel '24 circularlyslotted so that flexible drive shaft 3!, driven by motor 25, rotateswheel 24 in a forward direction when drive shaft 35 engages one side ofthe slot, and ma reverse direction on the other side of the slot. (For amore complete description of this type of drive see D. R. GoddardapplicationSerial Number 11,915, filed March 20, 1935.)

Rectified I. F. energy from detectors 8' and 9 operate solenoids 2i and28 to move armature 25. Arm 25 is pivoted at one end and is providedwith a forked bearing at the other end for engament with the shaft 3! soas to reversibly operate a clutch mechanism associated'there- -With.

An unbalance of currents in solenoids 21 and 28 causes armature 25 toshift shaft St to the forward or reverse engagement with wheel 24..

in general of my present invention, obtains its controlling energy fromthe differential detectors such as 8 and 9 of Figure 1. Thesedifferential detectors are fed cophasally by one of the signal or signalintermediate frequencies and antiphasally by the other. As long as thetwo signals are 90 degrees out of phase the plate currents of thedetectors 8 and 9 are balanced and no differential voltage is passed onto operate the controlling circuits. As soon as the relative phase ofthe two signals deviates from 90 degrees, the detector plate currentsare unbalanced and a differential voltage operates the controllingcircuits to correct the phase relation to 90 degrees.

More specifically, and referring to the differential detector diagram ofFigure 6 the two signal I. F.s are fed in at S1 and S2 to transformers 6and 1 respectively. Figures '7 and 8 show how the voltages fromtransformers 8 and I combine when the two signals are 90 degrees out ofp se. n, bu, T17 d A, (B7) Ru represent the vectors for tubes 8 and 9respectively. Voltage 1) is supplied from transformer l and voltage afrom transformer 6 to form the resultant r to be fed to tube 8. VoltageB is supplied from transformer I and voltage A from transformer 6 toform resultant R to be fed to tube 9. Thus, when the two signals are 90degrees out of phase the resultants R and r are equal and the detectedoutputs across resistors or equal impedances 8x and 9x would cancel toform zero voltage between leads B and B Figures 9 and 10 show the vectorrelations when one signal has shifted in phase so that the two signalsare no longer 90 degrees out of phase. The resultant r fed to tube 8 isgreater than the r R fed to tube 9. Consequently, the drops acrossresistors 8X and 9x will no longer balance and a voltage will be appliedto leads B and. 5 When the phase is shifted in the opposite directionthis differential voltage is reversed. Consequently, a voltage isproduced having a magnitude and direction dependent upon the relativephases of the two signals.

Referring again to Fig. l, the operation of my invention as thereinshown will be fairly well understood from the foregoing description.When the signals from the two antennae l and i deviate from a 90 phaserelationship the unbalance resulting in the differential detectors 8 and9 becomes effective in controlling one of the clutch solenoids 21 or 28of the phase shifter so as to cause the motor 26 to rotate the coil 21in the proper direction and through a suitable angle to restore thedesired 90 relationship between the currents in coils s1 and s2. Whenthe balance has been restored, the armature 25 is returned to itsneutral position, thus disengaging its associated clutch mechanism.

In some cases it may be found desirable to have the antennae combined ata phase other than 90 degrees. To do so the outputs of I. F. ampliher 5and coil 2| should be fed to couplin: tubes, their relative phaseadjusted, combined, and detected. Such a combining arrangement is shownin Figure 1a. The two signals (phase controlled to 90 degrees) would betaken from leads gxy, Hixy and llx lzxy of Figure l The signals in theseleads would then be adjusted to the desired phase of combination byphase shifter lx and combined through combining tubes ix and 5X intransformer Ex Detector Ixy detects the combined signals for utilizationin jack 8 The system illustrated in Figure 1 may be used for directionfinding by, for example, associating with shaft 22 a pointer P movableangularly with shaft 22, and a relatively stationary scale S. Theantennae l and l for this purpose should be spaced or be two directionalarrays of antennas.

'With such an arrangement, the pointer P would indicate on the scale thephase relation between the waves picked up upon l with respect to I. Byhaving previously calibrated the scale when in harbor, say, on knowndirections of several known transmitting stations, then, when at sea,deviation from the calibration would give deviation from the course.

If desired, by means of the Selsyn motors SMI, whose armature coincideswith shaft 22, and SM2 operating steering mechanism, guidance orsteering of a ship may be made automatic.

Incidentally, the system of Figure -1 is intended for operation withamplitude modulated waves. For reception of phase and frequencymodulated waves, leads fixy to Zry inclusive should be connected tosuitable phase or frequency modulation receivers, with, if desired, asuitable retardation circuit in either leads xy, lQxy OI Hxy, lzxy. V

In Figure 2, separate H. F. oscillators X6 and X4 are employed for thetwo superheterodyne receivers. The combined and detected energy is takenfrom detectors X8 and X9 via transformer Xl3. Switch XIZ adjusts forproper phase of audio frequency combination; the nor- I are cophasal.

mal position of this switch would be for parallel combination of the twodetector outputs. Oscillator X4 is held in the proper phase synchronismwith Xe to hold the output of I. F. amplifiers X and X5 in phasequadrature by means of energy furnished from the resistors X and XM inthe detector plate circuits. This differential voltage is applied tooscillator X4 which is an oscillator whose frequency is partly dependentupon its tuning and partly upon the control voltage applied to it. Acomplete description of oscillator X l and its frequency controllingcircuit is given in my copending application, Serial Number 616,803,filed June 13, 1932.

In the operation of receiver of Figure 2 the two I. F.s are held inphase quadrature by applying the controlling energy to one of the H. F.oscillators. This controlling voltage varies the frequency of the H. F.oscillator to obtain the proper 90 degree phase relation of the two I.F.s. The outputs of X5 and X5 may also be fed through 1aldS xy, iflxy,Xy, izxy to the combining circuit of Figure 1a for other than 99 degreecombination of the antennae as will be apparent from what has been saidbefore.

Briefiy, for varying the frequency of the oscillator 285 within dottedrectangle X4 of Figure 2, the output of the differential detector is fedthrough conductors X55 to a coupling tube 282 having a plate coil 286coupled to the tuned circuit 234 controlling the frequency of operationof the oscillator 23%. With a predetermined current flowing through tube282, the inductance of circuit 23 will be a certain value causing apredetermined frequency of operation of the local oscillator 23%. Withvariations in voltage both of value and sign across conductors Xl5, theimpedance, that is the impedance of tube 262 across coil 2% will vary,thereby changing the frequency of operation of the local oscillator 23%because of the change of effective inductance of tuned circuit 284.

The system of Figure 3 utilizes the same principle as the arrangement ofFigure 2 except that the individual I. F. energies are held in phasewith: (1) The combined I. F. energy (which would be portrayed if unit H!were a coupling tube fed through closed switch I?) (2) A locallysupplied I. F. oscillator contained in unit M (in which case switch I?would be open); (3) The filtered and limited carrier (switch closed).With unit It acting as a coupling tube according to (1), line l8 maycontain an artificial line or Wave filter to act as a retardationcircuit to allow the reception of frequency modulation in the manner ofthe receivers described in my copending application, Serial Number618,154, filed June 20, 1932. With unit l4 containing either the I. F.oscillator or carrier filter, a local carrier is available for thereception of phase and amplitude modulation. Automatic volume controlunit 19 operates on coupling tube units l3a, 53b, and i3c, via lead 20,to maintain the volume of the combined energy constant.

Generally, in connection with Figure 3, differential detectors Ea, 8a,"5b, 8b, 7c, 80, act so that the outputs of coupling tubes l3a, |3b-,and |3c The combined cophasal output of lw, i311, |3c is fed toantiphasal transformer 2|, and the output of unit U5 is fed to cophasaltransformer 22 of detectors 23, 24. Phase shifter 28 serves to adjustthe currents fed to 22 and 2| so as to be of correct phase relationshipfor audio frequency detection.

The receiver of Figure 3 is an elaboration of the fundamental ideacontained in the receiver of Figure 2 except that the signals are allheld in phase quadrature with a standard instead of with each other.This standard, as before stated, may be an I. F. oscillator or thefiltered and limited carrier; it may also be the combination of thesignals. With this sort of an arrangement, since the signals would allbe combined in phase quadrature with the standard,

they would be in phase with each other so that the combining circuit ofFigure la would only be necessary for other than in phase combination.Referring in greater detail to the circuit of Figure 3, the standard(consisting of an I. F. oscillator, the filtered carrier, or thecombined signals) is fed to the differential detectors via cophasaltransformers 6a, 6b, and 6c. The three signals at I. F. are fed viaantiphasal transformers 5a, 5b and 5c. The controlling energy from thedifferential detectors is utilized to automatic frequency control the H.F. oscillators to maintain the proper frequency and phase, forcombination, of all of the I. F.s. The three I. F.s are passed throughcoupling tubes |3a, |3b and |3c to the automatic volume control detectorl9 and to the audio detectors 23, 24. The

automatic Volume control may be made to regu- 9 late the volume of thetotal combined signal or the separate coupling tubes as shown in thediagram of Figure 3 or the individual radio frequency amplifiers in themanner of the antenna choosing diversity system as described in U. S.Patent 2,004,128, granted June 11, 1935 to H. 0. Peterson. For phasemodulation and relatively increased carrier amplitude modulationreception, unit I4 would be an I. F. oscillator, or a carrier filter andlimiter fed by closing switch H. For frequency modulation a phaseretardation circuit whose output phase is linearly proportional to itsinput frequency would be inserted in line l8 and unit I4 would act as acoupling tube to couple the combined energy to the differentialdetectors as a standard, and to the audio detectors via line Hi.

When receiving amplitude modulated waves in the arrangement shown inFigure 3, unit It may be a local oscillator, in which case phase shifter28 is adjusted so that either tube 23 or 24 is excited cophasally, inwhich case, too, the outputs of 23, 24 are switched by switch 25 inpush-pull.

In the alternative, for amplitude modulated waves with unit M anoscillator, phase shifter 28 may be adjusted so that currents in 22 and2| are 90 degrees apart and switch 25 thrown for parallel feed of theprimaries of transformer 26.

The foregoing remarks concerning adjustment apply for reception ofamplitude modulated Waves when unit I4 is made a carrier filter andlimiter. However, when unit it is merely a coupling system whose outputis the combined signal, only line l5 or only line l8 should feeddetectors 23 and 24. Also, in either of the latter instances theprimaries of transformer 26 should be in parallel.

When receiving frequency modulated Waves, assume unit It has an outputequal to the combined signals. Shifter 28 should be adjusted for 90degrees phase difference in currents in 2| and 22 and, moreover, aretardation circuit should be placed in line I8.

When utilizing the system of Figure 3 for reception of phase modulatedwaves, unit l4 should be operated only as a carrier filter or carrieroscillator. By means of phase shifter 28, the currents in 22 and Elshould be displaced degrees and the primaries of transformer 26, assumedto be wound in the same direction, should be connected in push-pull.

It should be noted that by using correction circuits, the frequencymodulation adjustment may be used for phase modulation reception andthat frequency modulation reception may be carried on with the phasemodulation adjustment. Thus, by putting a circuit across 2'! whoseoutput is inversely proportional to the input frequency, the system ofFigure 3 adjusted for frequency modulation reception will operate togive true reproduction from received phase modulated waves.

By connecting a circuit to 21 whose output varies linearly with theapplied input, the receiver will, with a phase modulation adjustment,faithfully reproduce the signal from received frequency modulated waves.

In the system of Figure 4, the triple detection superheterodynereceivers i, 2, 3, 4, 5, 6, 7 and I, 2, 3, i, 5, 6, i use a common highfrequency oscillator i and separate I. F. oscillators 6 and 8'.Oscillator 5 is frequency controlled from the differential detectors 9and I0 which are fed antiphasally by the intermediate frequency energyfrom one receiver and cophasally by that from the other receiver. Thiscontrol may be done in a manner similar to that for oscillator X4 ofFigure 2. Coupling tube units 1 and 'i separate the controlling energyand the energy combined for utilization in detectors I8 and I9. Phaseshifter 25 adjusts the phase of combination of the two energies for uilization. Automatic frequency control such as described in Figure 2 isapplied Via line i to the high frequency oscillator 4. Unit I5 containsa crystal filter, limiter, and phase shifter for phase and amplitudemodulation reception and an artificial line or wave filter for frequencymodulation reception. The detection in this receiver incorporates theprinciples given in my copending application, Serial Number 616,803,filed June 13, 1932.

In operation the circuit of Figure 4 utilizes the same principle as theone of Figure 2 except that the second oscillator of a triple-detectionsuperheterodyne is frequency controlled to maintain the proper phasesynchronism. The circuit is shown with an automatic-frequency-controlcrystal-filter detecting circuit, but could be used on any otherdetecting arrangement for any type of modulation. Since the two signalsare held in phase quadrature, the phase adjuster 25 is necessary forcombinations at other than 90 degrees.

The system of Figure 4 is suitable for amplitude frequency and phasemodulation reception, it being noted that for phase and amplitudemodulation reception adjustments are made as prescribed for Figure 3.For frequency modulation reception, unit iii of Figure 4 should be aretardation circuit.

In the system of Figure 5, triple detection superheterodynes areutilized and the intermediate frequency energies are held in phase byinserting an artificial line or wave filter i in one I. F. circuit andapplying the difierential voltages from detectors l8 and H to frequencycontrol the common second I. F. oscillator 6.

The audio output is taken from transformer l5.

In the circuit of Figure 5 the phase adjustment is obtained by using thedifferential detector controlling energy to vary the frequency of thecommon second oscillator of the triple detection superheterodynes andinserting a retardation circuit 1 in one of the second I. F. circuits.Thus, as the second I. F. is varied, the phase of the I. F. through theretardation circult is changed relative to the one not through theretardation circuit and the phase adjustment is obtained. Thisretardation circuit could also be inserted in series with the leads fromoscillator 6 to amplifier 5 so that the modulated signal would not haveto pass through it.

The system of Figure 5 is suited for amplitude modulation reception. Forphase and frequency modulation reception, the primaries of transformers8 and 9 should be made to feed into suitable phase and frequencymodulation re ceivers.

Although my present invention has been described in connection with adiversity receiving system, its use need not be limited to such anapplication. The fundamental idea gives a receiver which automaticallycorrects the phase relation between two receiver outputs. Consequently,as already shown, it may be used in a direction finder whereby thecontrolling energy operates a meter to indicate the bearing of thereceived. station and it may also be used as a radio control for mobilecraft in which the controlling energy operates the steering apparatus sothat the craft will be guided on a given bearing with relation to thereceived signal.

Also this system may be used for frequency diversity. For example, thecircuits of Figures 1, 2 and 3 may be used to hold two signals ofdifferent radiation frequency in frequency and phase synchronism at I.F.

Moreover, although most of the circuits have been drawn to utilize onlytwo antennae, it will readily be apparent that any number of antennaemay be used by a continuation of the same ideas given herein.

Having thus described my invention, what I claim is:

1. The method of reducing fading of radio signals which includes makinga plurality of signal energy collections, producing and maintaining apredetermined phase displacement in the energies collected, combiningthe phase displaced energies, detecting the combined phase displacedenergies and translating the detected energies.

2. The method of reducing fading of radio signals which comprises makinga plurality of signal energy collections, producing a predeterminedphase displacement in the energies collected, combining the phasedisplaced energies, maintaining the phase displacement substantiallyconstant before combination despite variations in phase of the receivedenergies during their collections, detecting the combined energies, andtranslating the detected energies.

3. The method of receiving radio signals which comprises separatelyreceiving said signals, combining the signals in pretermined phasedisplacement, detecting the combined signals, utilizing the voltagevariations of the detected signals to maintain the predetermined phasedisplacement of the collected energies before combination and utilizingthe detected combined energies for signal translation purposes.

4. The method of reducing fading of radio signals which includesseparately receiving said signals, producing and maintaining a degreephase displacement in the signals received, combining the signalsdisplaced 90 degrees, detecting the combined signals and-translating thedetected signals.

5. The method of reducing fading of radio signals which comprisesseparately receiving signal energies, producing a 90 degree phase shiftin the separately received signal energies, maintaining the 90 degreephase relationship despite relative variations in phase of the receivedsignal energies, combining the energies displaced in phase by 90degrees, and detecting and translating the combined energies.

6. The method of receiving radio signals which comprises separatelyreceiving signals, combining said received signals, detecting saidcombined signals, and utilizing the voltage variations of said combineddetected signals to maintain a substantially constant phase differencebetween the received signals before combination.

7. The method of receiving radio signals which comprises separatelyreceiving said signals, producing a 90 degree phase displacement betweensaid received signals, combining the phase displaced signals, detectingthe combined signals and utilizing the voltage variations of saiddetected combined signals tomaintain the 90 degree phase displacement ofthe combined signals.

8. The method of reducing fading which includes making a plurality ofsignal energy collections, heterodyning the collected energies to acommon different frequency, producing and maintaining a predeterminedphase shift in the different frequency energies, combining the phaseshifted energies, detecting the combined energies and translating thedetected energies.

9. The method of reducing fading of received radio waves which includesheterodyning the received waves to a different frequency, producing a 90degree phase displacement between the different frequency energies,combining the energies displaced 90 degrees, utilizing the combinedenergies to maintain the 90 degree phase displacement of the differentfrequency energies, and translating the combined phase displacedenergies.

10. Apparatus for reducing the fading of received radio waves comprisinga pair of antennae for collecting transmitted waves, a differentialdetector, means for feeding energies collected upon one antennacophasally to the differential detector, means for feeding energiescollected upon the other antenna, antiphasally to said differentialdetector, means for maintaining a predetermined phase displacementbetween the energies respectively fed to said differential detector, thelast said means being responsive to an unbalancing of the output fromsaid detector, and means for translating and utilizing the output ofsaid differential detector.

11. Apparatus for receiving radio waves comprising a pair of antennae, adifferential detector, means for feeding energy collected upon oneantenna cophasally to said differential detector, means for feedingenergy collected upon the other antenna antiphasally to saiddifferential detector, means for maintaining a predetermined phasedisplacement between the energies fed to said difierential detector, andmeans for translating the output of said differential detector.

12. A radio receiving system comprising a pair of antennae, means forheterodyning the energies collected upon the antennae to an intermediatefrequency, a differential detector, means for feed ing the intermediatefrequency energy from one antenna antiphasally to said differentialdetector, means for producing a phase shift of substantially 90 degreesin the intermediate frequency energy from the other antenna, means forapplying the phase shifted energy cophasally to said differentialdetector, and means responsive to the output of said difierentialdetector for maintaining the phase quadrature relationship between theintermediate frequency energies.

13. A receiving system comprising a pair of antennae, means for beatingenergies collected upon one antenna down to an intermediate frequency, alocal oscillator associated with the other antenna for beating the wavescollected thereon down to the same intermediate frequency, means forcombining the intermediate frequency energies, and means responsive tothe combined energies for so varying the frequency of said oscillator asto maintain a predetermined phase displacement between the intermediatefrequency energies.

14. A receiving system comprising a pair of antennae, a pair ofoscillators for beating the energies collected upon said antennae downto a common intermediate frequency, and means for so varying therelative frequencies of said local oscillators as to maintain apredetermined phase displacement of the intermediate frequency energiesdespite variations in phase of the energies collected upon saidantennae,

15. A receiving system comprising a pair of antennae, a pair ofoscillators for beating the energies collected upon said antennae downto a common intermediate frequency, means for combining the intermediatefrequency energies, and means responsive to the combined energies forvarying the relative frequencies of operation of said oscillators forsubstantially maintaining phase quadrature between the intermediatefrequency energies.

16. In combination, a pair of antennae, a differential detector, a pairof oscillators, means for beating energies collected upon the antennaeand energies from the oscillators so as to produce intermediatefrequency energies, means for feeding intermediate frequency energy fromenergy collected upon one of the antennae antiphasally to saiddifferential detector, means for feeding in termediate' frequency energyderived from energy collected upon the other antenna cophasally to saiddifferential detector, and means responsive to the output of saiddifferential detector to so vary the frequency of oscillation of one ofsaid oscillators as to substantially maintain phase quadrature betweenthe intermediate frequency energies fed to said differential detector.

1'7. In combination, a plurality of radiant energy collecting antennae,a receiving network for each antenna, means including a differentialdetector for combining the energies from said networks, a balancedtwo-way utilization circuit connected to said differential detector, andmeans including a phase correcting device operative in accordance withtransient departures from a balanced condition in said utilizationcircuit for maintaining substantially constant the phase relationshipbetween the energies respectively impressed upon said differentialdetector by each of said receiving networks.

MURRAY G. CROSBY.

